MODULATION OF TISSUE-TYPE PLASMINOGEN-ACTIVATOR BY RETINOIDS IN RAT PLASMA AND TISSUES

In this study the effect of vitamin A status and retinoid treatment on the activity of tissue-type plasminogen activator (TPA) and its inhib itor, plasminogen activator inhibitor-type 1 (PAI-1), in plasma and in several tissues was investigated in BN/BiRij rats. Hypervitaminosis A and retinoic acid treatment increased plasma TPA activity by approxim ately 50%, but PAI-1 activity was not affected. The effect of retinyl palmitate treatment on plasma TPA activity was already significant aft er 5 days and continued for at least up to 8 wk. Isotretinoin treatmen t affected neither plasma TPA nor PAI-1 activity. In plasma of vitamin A-deficient rats, TPA activity was decreased by a factor of three, wh ereas PAI-1 activity was increased twofold. Modulation of plasma TPA a ctivity by vitamin A status and retinoic acid treatment was associated with similar changes in tissue TPA activity. This suggests that the c hanges in plasma TPA activities might be the result of changes in tiss ue TPA synthesis.